Bacteria that cause plaque and tartar build up live on your teeth. Every time you eat you are feeding the bacteria as well as yourself. Once the bacteria have been fed, they produce a very strong acid that eats away at the enamel on your teeth.
If you don’t remove this layer of plaque by brushing and flossing, the bacteria will keep destroying your tooth structure until you get a hole in your tooth. These holes are known by many names, such as tooth decay, cavities, and dental caries and can be deep enough to expose the root of your tooth and cause further damage.